1. Field of the Invention
The present invention relates to a control apparatus for an electric motor and an abnormality detection method for electric motor control. More specifically, the invention relates to detection of abnormality in electric motor control by a control apparatus configured with a plurality of electronic control units (ECUs).
2. Description of the Background Art
In controlling an electric motor including an electric motor that is mounted on a hybrid vehicle for generating wheel driving power, it is required to control the output of the electric motor according to an operational command value. Further, when abnormality occurs in electric motor control, it is necessary to immediately detect the abnormality and take appropriate measures.
In view of this, regarding a hybrid vehicle provided with an engine and an electric motor as mechanical power sources for driving the vehicle, Japanese Patent Laying-Open No. 10-285710 (hereinafter Patent Document 1) for example discloses an abnormality detection apparatus for the hybrid vehicle that uses a torque sensor to detect abnormality of the mechanical power sources with high precision.
The abnormality detection apparatus for the hybrid vehicle disclosed in Patent Document 1 determines whether or not abnormality of the mechanical power sources occurs depending on whether or not a difference between a target torque of the vehicle driveshaft and an actual torque detected by the torque sensor is larger than a predetermined reference value. Further, in the case where there is abnormality, based on an actual throttle opening position and an actual motor current value as well as their command values, it is determined which of the engine and the motor generator has the abnormality. Thus, using the torque sensor, abnormality of the mechanical power sources can be detected with high precision and the configuration can be provided at a lower cost as compared with the case where the engine and the motor generator are provided with respective torque sensors.
As for a control apparatus for an electric motor, the control apparatus is generally configured with an electronic control unit (ECU) including a digital computer performing operations according to a predetermined program. However, because of limitations of the operation speed and the throughput, there could be the case where the configuration having a single electronic control unit for performing the overall electric motor control including the above-described abnormality detection is inefficient.
In such a case as described above, a configuration employed for the control apparatus includes separate ECUs that can communicable with each other and that are respectively used, for example, to perform actual electric-motor drive control which is required to be high-speed control and to generate an operational command value for the electric motor based on an operational request and perform abnormality detection control. For example, a plurality of ECUs may be configured in hierarchical form to efficiently configure a control apparatus for an electric motor while the throughput and the operation speed as required for each ECU are kept moderate.
Such a control apparatus generally has a control configuration in which an operational command value (typically torque command value) for the electric motor that is generated by an ECU at a higher level (hereinafter also referred to simply as high-level ECU) is transmitted to an ECU at a lower level (hereinafter also referred to simply as low-level ECU) and then the low-level ECU performs actual motor drive control.
Here, with the purpose of sophisticating the electric motor control, if it is tried to implement a control configuration with which the operational command value can additionally be corrected according to actual electric-motor operation, preferably the low-level ECU performs highly responsive processing for enhancing the effect of such correction. This control configuration adjusts both of an operational command value generated by the high-level ECU and the additional operational command value generated by the low-level ECU so as to generate an operational command value which is the final one for electric motor control.
However, in the control configuration as described above, the high-level ECU that should essentially detect abnormality in electric motor control cannot directly know the final operational command value for the electric motor control. Therefore, the accurate abnormality detection for electric motor control could be hindered.
Further, regarding a control apparatus configuration which may not particularly be hierarchical and in which respective operational command values independently generated by a plurality of ECUs are taken into consideration to set a final operational command value, it is required that one of the ECUs accurately detects abnormality.